Crushed rock is typically used for many construction applications. Crushed rock is often used as a lower layer for the construction of roads, pavement, and highways. The crushed rock may be spread over the ground, and asphalt or concrete may be applied over the top of the layer of crushed rock.
The crushed rock is often mined from rock quarries. Large rock is crushed and broken into smaller rock particles. During the processing of the larger rock into the crushed rock, dust, fines, and small particulate matter is inherently produced. Many road construction projects require that the crushed rock only contain a minimum level of this “fine” material. Crushed rock that contains too much of this fine material may be rejected as being out of specification. Typically, many road construction projects require that the crushed rock have a content of no more than approximately 5% fine material. The excess fine content in the crushed rock results in an increased amount of oil needed in the asphalt. If the crushed rock contains an excess amount of the fines, then the entire shipment of the crushed rock may be rejected.
Previous attempts to remove fines or lower the fine content of crushed rock have involved expensive and difficult to maintain equipment. Moreover, many of the prior art attempts and designs to remove the fines from the crushed rock results in excessive waste by-products. For example, one such prior art device to remove fines from the crushed rock includes an air separation device. The air separation device uses large fans and turbines to blow the fines from the crushed rock. The fines are collected in receptacles that allow the blown air to pass through. However, the blowing of the fines degradates the fans and turbines of such air separation devices. Constant maintenance and replacements of such fans and turbines is required.
Other attempts to remove the fines from the crushed rock involve the use of log washers. The crushed rock and fines are washed in the log washers with water in order to separate the fines from the crushed rock. The fines typically float, and the fine and are washed from the heavier crushed rock particles. However, the use of the log washers results in waste pools of water containing the fines. Also, the now wet fines removed by the log washer may require additional drying steps or processes before the fines can be used as a material for certain applications.
Also, conventional wet or dry vibrating screens with very fine openings are employed to remove the fines from the crushed rock. Unfortunately, the screens used in the dry screening process have very fine openings, which tend to plug with rock material. Force-drying the fines and crushed rock, prior to the dry screening, alleviates some of problems with the plugging of the openings of the screen, but this step requires additional equipment and labor. Wet screening results in some of the similar discharge water problems as encountered with log washing. As such, the wet and dry screening processes are problematic for various reasons.